(1) Field of the Invention
This invention relates to a power switching unit of a portable telephone operated with a battery and more particularly to a power switching unit of a portable telephone having a storage function of data such as telephone numbers.
(2) Description of the Related Art
Recently, as the demand for mobile communication has increased, high functions and high performance as well as a simple radiotelephone function are required for a portable telephone.
One of the high functions is a storage function which enables the portable telephone to store data such as telephone numbers and names for reading out the data. This function is called xe2x80x9celectronic pocket notebook functionxe2x80x9d in this specification.
With such a portable telephone, if the output voltage of an internal battery falls below the threshold voltage required for a radio unit to operate at the minimum, power supply from the battery is shut off to stop all functions of the portable telephone in order to prevent the radio unit from operating abnormally.
In such a portable telephone, the electronic pocket notebook function section consumes much less power than the communication function section. If the battery output voltage drops and operation of the communication function becomes impossible, often the electronic pocket notebook function can be used. Formerly, however, when the battery output voltage dropped, power supply was stopped not only to the communication function section, but also to the electronic pocket notebook function section. Thus, the electronic pocket notebook function as well as the communication function became unavailable.
Accordingly, it is an object of the invention to provide a power switching unit of a portable telephone having a data storage function such as an electronic pocket notebook function that can be used even if a supply voltage from a battery drops.
To the end, according to a first embodiment of the invention, there is provided a power switching unit of a portable telephone comprising a radio unit and a control unit which contains a data storage function and controls operation of the radio unit, the power switching unit comprising:
a battery for supplying power to the control unit and the radio unit;
first voltage monitor means for monitoring a supply voltage of the battery to output a first voltage drop signal when the supply voltage falls below a first predetermined value; and
communication disconnection means for stopping power supply to the radio unit upon reception of the first voltage drop signal.
The power switching unit of the portable telephone further includes voltage adjustment means for adjusting the voltage suppled to the control unit from said battery to a predetermined operating voltage of the control unit for supplying it to the control unit.
According to a second embodiment of the invention, there is provided a power switching unit of a portable telephone comprising a radio unit and a control unit which contains a data storage function and controls operation of the radio unit, the power switching unit comprising:
a first battery for supplying power to the control unit;
a second battery normally for supplying power to the radio unit;
first voltage monitor means for always monitoring a supply voltage of the first battery to output a first voltage drop signal when the supply voltage of the first battery falls below a first predetermined value;
power supply instruction means for outputting a power supply instruction signal upon reception of the first voltage drop signal;
power supply means for supplying power to the control unit from the second battery upon reception of the power supply instruction signal;
second voltage monitor means for always monitoring a supply voltage of the second battery to output a second voltage drop signal when the supply voltage of the second battery falls below a second predetermined value;
power disconnection instruction means for outputting a power disconnection signal upon reception of the second voltage drop signal; and
power disconnection means for stopping power supply to the radio unit from the second battery upon reception of the power disconnection signal.
If the voltage supplied from the battery drops, power supply to the radio unit is shut off, but power supply to the control unit having the data storage function is continued, so that the user can use only the data storage function such as the electronic pocket notebook function.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.